The principle of antituberculosis therapy is to apply a combination regimen of at least two bactericidal drugs to which the bacteria are susceptible for sufficient duration, thus improving the efficacy of the therapy and preventing the development of resistant strains. If a certain side effect develops during the therapeutic trial, the next step includes identifying the causative drug, estimating the type and magnitude of the side effect, and finally deciding whether the regimen should be discontinued. In a clinical setting, however, these decisions cannot be made easily. Many antituberculosis drugs causes similar side effects, and even if the causative drug is identified, the decision to discontinue the drug must be based on its relative importance in the current antituberculosis regimen. Effective application of antituberculosis medication requires the physician to fully understand what adverse effects each drug is associated with, which side effect necessitates withdrawal of the drug, and how to rechallenge the drug with side effects when it is absolutely required in the regimen.